GlcNAc is a monosaccharide in organisms and widely exists in bacteria, yeasts, molds, plants and animals. In human bodies, GlcNAc is a synthetic precursor of a glycosaminoglycan disaccharide unit and plays an important role in repair and maintenance of cartilage and joint tissue functions. Therefore, GlcNAc is widely used as a drug and a nutrient dietary additive to treat and repair joint damage. In addition, GlcNAc also has many applications in the field of cosmetics. At present, GlcNAc is mainly produced by acid hydrolysis of chitin in shrimp shells or crab shells, waste liquid produced by the method has relatively serious pollution to the environment, and a resulting product is prone to allergic reactions and not suitable for people who are allergic to seafood to take.
Bacillus subtilis is widely used as a production host for food enzyme preparations and important nutrient chemicals, and products thereof are certified by FDA as “generally regarded as safe” (GRAS) safety class. Therefore, adopting metabolic engineering methods to construct recombinant Bacillus subtilis is an effective way to produce food safe grade GlcNAc. However, the GlcNAc titer and yield on glucose of recombinant Bacillus subtilis (BSGNY-Pveg-glmS-P43-GNA1) still cannot meet the requirements of industrialization, and therefore it is necessary to further increase the production capacity of the recombinant Bacillus subtilis. Glucose enters the glycolysis pathway and the pentose phosphate pathway after entering cells. At the same time, the synthesis of peptidoglycan also utilizes a part of glucose. In order to further increase the titer and yield of GlcNAc, it is necessary to reduce the flowing amount of glucose to these pathways. However, these pathways play an extremely important role in cell growth, and direct blocking these pathways inevitably affects cell growth. Therefore, these pathways need to be dynamically regulated and controlled to achieve a balance between cell growth and product synthesis. At the same time, xylose, serving as the main product of hydrolysis of lignocellulose, is the most abundant saccharide in nature except glucose, but most microorganisms have a weaker utilizing capacity on xylose, and the co-utilizing of glucose and xylose also has big problems. If a production strain which can efficiently co-utilize glucose and xylose is constructed, the production strain can utilize a renewable biomass resource for synthesis of a target product. In the previous work, the co-utilizing of glucose and xylose in the B. subtilis was achieved through the elimination of the regulation and control of xylose metabolism, that is, the expression of transport protein araE in the B. subtilis was enhanced and a xylose metabolism pathway gene xylAB from Escherichia coli was expressed (Reference literature: CHEN T et al. Engineering Bacillus subtilis for acetoin production from glucose and xylose mixtures [J]. Journal of Biotechnology, Elsevier B.V., 2013, 168(4): 499-505.). However, in their work, only the metabolism pathway of xylose was strengthened, and the metabolism of glucose was not regulated and controlled. When the cells can use both glucose and xylose, more glucose can be introduced into the synthesis pathway of the target product to avoid the waste of carbon resources.